1. Field of the Invention
The present invention relates to an image recording apparatus which uses a solid recording device array for recording images. The invention may be used in image recording apparatuses such as photocopiers, facsimiles, printers, and so forth.
2. Description of the Related Art
In recent years, a self-scanning recording chip which has functions for scanning solid recording devices contained within the chip has been proposed. FIG. 4 shows an example of this, illustrating an equivalency circuit of a self-scanning LED chip wherein 128 light-emitting devices are arrayed.
In FIG. 4, L1 through L128 denote light-emitting thyristors serving as light-emitting devices, S1 through S128 denote sending thyristors, .phi.I denotes a signal line wherein pixel data corresponding to the 128 light-emitting devices is serially input, .phi.SS denotes a signal line for input of a start signal instructing the LED chip to begin operating, and .phi.S1 and .phi.S2 denote signal lines for input of shift signals for sequential shifting of the devices which are to emit light. The operation of the self-scanning LED chip will be described with reference to the timing chart shown in FIG. 5.
First, the start signal line .phi.SS is set from L to H (t1). At the next timing, the shift signal .phi.S1 is changed from H to L, thereby turning the sending thyristor S1 on (t2), and the gate voltage thereof is anode potential, i.e., approximately 5V. Now, setting .phi.I to L causes the recording thyristor L1 to emit light (t3), and changing it to H extinguishes the light (t4). If .phi.I were left at H, the recording thyristor L1 would not emit light during the period from t3 to t4.
Next, the shift signal .phi.S2 is set from H to L, thereby turning the sending thyristor S2 on (t5). At the next timing, changing the shift signal .phi.S1 from L to H turns the sending thyristor S1 off (t6), and thus a sending thyristor in the on state is S2 only. Now, setting .phi.I to L causes the recording thyristor L2 to emit light (t7), and changing it to H extinguishes the light (t8). If .phi.I were left at H, the recording thyristor L2 would not emit light during the period from t7 to t8.
Next, the shift signal .phi.S1 is changed from H to L, thereby turning sending thyristor S1 on (t9). At t10, the shift signal .phi.S2 is switched from L to H, turning sending thyristor S2 off. Setting .phi.I from H to L at t11 causes recording thyristor L3 to emit light, and changing it to H extinguishes the light at t12.
Repeatedly performing the above operations sequentially scans the 128 sending thyristors S1 through S128, and the recording thyristors L1 through L128 which correspond with each of the sending thyristors emit light in accordance with the pixel data which is input to .phi.I.
Next, FIG. 6 shows the flow of pixel data in the driving control unit of a known self-scanning LED chip. In FIG. 6, 30-1 through 30-n denote the aforementioned self-scanning LED chips, each including recording thyristors L1-L128, as shown for LED chip 30-1. Reference numerals 40-1 through 40-n denote the shift registers, each 128 bits, and 50-1 through 50-n denoted latch circuits for latching the 128 pieces of pixel data corresponding to the self-scanning LED chips 30-1 through 30-n. Reference numerals 60-1 through 60-n identify driver units for driving self-scanning LED chips 30-1 through 30-n, respectively. The following is a description of the operation thereof.
First, the first line of pixel data, 128.times.n pieces, is input from the signal line .phi.1 which is 1 bit in width. This pixel data line is sequentially input to the shift registers 40-1 through 40-n. Once all 128.times.n pieces of pixel data are input to the shift registers 40-1 through 40-n, the latches 50-1 through 50-n corresponding to the respective shift registers each latch 128 bits of pixel data, following which the second line of pixel data is input to the shift registers 40-1 through 40-n. On the other hand, the latch circuits 50-1 through 50-n serially transfer the 128-bit pixel data held within each respective self-scanning LED chip 30-1 through 30-n, one bit at a time.
Then, as described above, the recording devices are sequentially scanned within each LED chip 30-1 through 30-n, and selectively emit light according to the pixel data which is being sent.
Thus, with this arrangement, each recording device is subjected to time division. Hence, when driving, it becomes necessary to have enough shift registers to convert an entire line of serially-input pixel data into parallel data and output it, and latch units for latching the entire line of pixel data and outputting this to each corresponding recording chip. This latching increases the cost of the recording head. Likewise, the larger number of signal lines connecting the shift registers and the latches have led to high costs.